Merge pull request #268 from heroku/fix-url-npm-faq

Update URL for "node_modules checked into source control"

lib/failure.sh

@@ -49,7 +49,7 @@ warn_node_engine() {
 warn_prebuilt_modules() {
   local build_dir=${1:-}
   if [ -e "$build_dir/node_modules" ]; then
-    warning "node_modules checked into source control" "https://www.npmjs.org/doc/misc/npm-faq.html#should-i-check-my-node_modules-folder-into-git-"
+    warning "node_modules checked into source control" "https://docs.npmjs.com/misc/faq#should-i-check-my-node-modules-folder-into-git"
   fi
 }